Surging Idle While In Gear

[glenmore]

I need some help in diagnosing a problem from a distance.

Some background:

1990 LS400, about 160,000 miles. I've had some the typical suspension issues but the engine has been near perfect.

I am in Los Angeles. In preparing the car for my daughter to use in San Francisco, I just did plugs, new wires , caps and rotors. While I had the MAF out, I spritzed it with cleaner. I finish up and start the car, it revs to 1000 for about a minute to warm up, then the rpms drop to 400 and then to 0 and the car stalls out. I curse. I check my work. I try again and the car runs normal a bit longer before choking and dying. The next day I take it to a tire shop to align the front end (I also changed tie rods). The shop is close by and I hope to align the wheels so I can then try and nurse the car to my indie. The car runs perfect. I'm guessing that maybe I was too heavy handed with the cleaner and maybe the MAF finally dried out. I drive the car out to the indie (about 15 miles) to leave it so he can start first thing in the morning and again the car runs perfect. Of course the cars behaves at the indie so all he does is change the fuel filter, cleans the throttle body and runs some injector cleaner thru the car. I pick up the car, runs fine. My wife drives the car about 400 miles from LA to San Francisco with no issues. My daughter drives it a few days and no issues. Then today, she is idling at a stop, foot on the brake, and the engine surges in waves up to about 2000 rpm. She holds the car back with the brakes. Then the rpms drop back to a normal 400 and everything is fine. She did not note any idiot lights.

Any ideas? And any suggestions for a reputable shop in the San Francisco area?

Thanks,

glenmore

1990 LS400

1991 300CE

2000 C280

[VMF]

hows that famous wiring harness in the trunk?

[glenmore]

I am going to have her check that. Is it only on the left side or is there wiring on both sides?

Thanks,

glenmore

[Alexander the o.k.]

I am going to have her check that. Is it only on the left side or is there wiring on both sides?

Thanks,

glenmore

Any other symptoms, weird behavior?

Did you check the TPS?

The fact that it happened after working on those areas leads me to suspect that is where the problem lies. But it could be coincidence. Where is wwest when ya need him? :) .

Here ya go: http://us.lexusownersclub.com/forums/index...showtopic=50087

"This same type of problem happened to me about a year ago. This smooth world class car started balking, cutting out, lurching, wild rpms, dash flickering, radio went out when hitting the brakes, just seemed ready for the junk yard. It happened all of a sudden. No warning.

I thought the engine was toast.

Now it's smooth as silk w/ 255,000 miles on it.

Open the trunk. On the left side you will see a wire harness on the left hinge. After repeated openings and closings the wires inside that harness become fatigued and frayed. Then they start shorting out. Then sputtering, stalling, and everything you describe. This is a design flaw and lexus knows it.

If this describes your problem, then remove the plastic bracket on the left hinge, strip down the harness, untwist all the wires, re-connect, then re-tape.

Make sure to leave off the hinge bracket that ensures tension on the harness. Just let the whole mess swing free and loose.

In my case, problem solved, and no spending thousands of dollars in diagnostics, parts, and tech snafus.

Best of all, it's free. Takes about 30 minutes."

[glenmore]

No other wierdness or symptoms so far. Just this one instance of sudden revving.

I told her to take the car to an empty lot and drive a bit and see if it would happen again and to note anything else like idiot lights, etc.

After my repairs, the RPMs at idle seemed to be a tad low. It sits just above 400. From the Lexls site, this seems low. Would this be caused by a fading TPS?

I take it that my indie must have handled this part when he cleaned the throttle body and may have "hurt" it when removing or re-installing or it may have been on the way out anyways.

Thank you for your input,

glenmore

[Alexander the o.k.]

I think there should be an adjustment slot on it.

It should be loosened, then adjusted, then set/ retightened at the sweet spot. Anyone have pics of the apprx. position in the slot it should be set at? Go by sound of revs and smoothness to get you close, initially.

Anyway, if someone has em, it should be piece of cake. Or you could have someone watch the tach while adjusting it.

There may even be a tutorial on it somewhere. search the term.

For my 1st gen, cold idle is around 1100. Warm idle is around 600-700.

[python]

tps are checked with an ohm meter....there is a specific way to check this, do not loosen then eyeball it or try to find some sweet spot.....geezus people! put it in place then u put a certain size shim between the stop and the throttle cable lever and measure ohms between certain contacts on the tps ......get the instructions online.... just google it

[python]

it could be an IAC motor

[Alexander the o.k.]

tps are checked with an ohm meter....there is a specific way to check this, do not loosen then eyeball it or try to find some sweet spot.....geezus people! put it in place then u put a certain size shim between the stop and the throttle cable lever and measure ohms between certain contacts on the tps ......get the instructions online.... just google it

Does it sound like she's got an ohm meter in her purse? Or knows what one is? Or the correct tolerances?

I'm trying to set dad on the right track here.

Set the damn thing close, and get it into a shop. Tell the tech: TPS. Back charge the old tech. Done.

Pics would help tho.

Search threads using throttle position sensor.

Did you python, read the damned post?

Key-rist.

[python]

then dont mess with it, take it to someone who knows what they are doing....shes in san fran and her dad is in LA and u r telling this person to have his daughter to go buy a tps (with out having it checked) and to put it on herself! lmfao, that spells disaster, she has no idea what shes looking at....so before u get all butt-hurt, think before you post and give some rediculous advice

[glenmore]

I appreciate all the comments and suggestions. My daughter had another two incidents, identical to the one I experienced on the first start after all the repairs I did. The car idles low (about 400) and almost dies. In one case she let off the brakes and the car inched forward and idling resumed, in the second case she shifted into neutral and that was enough to keep rpms up to avoid stalling.

I checked the price of a new idle air control valve, about $1000! Yikes!

I'm going to have her take it into a shop and hope for the best.

Thanks all,

glenmore

1990 LS400

[GX2008]

If she made a certain stop, she probably stepped on the brake and gas at the same time. It happened to me 2 times. I had to shift to "Neutral" once and turn off the car the other time. I was scared to drive but was able to duplicate it recently.

Some background:

1990 LS400, about 160,000 miles. I've had some the typical suspension issues but the engine has been near perfect.warm up, then the rpms drop to 400 and then to 0 and the car stalls out. I curse. I check my work. I try again and the car

I am in Los Angeles. In preparing the car for my daughter to use in San Francisco, I just did plugs, new wires , caps and rotors. While I had the MAF out, I spritzed it with cleaner. I finish up and start the car, it revs to 1000 for about a minute to runs normal a bit longer before choking and dying. The next day I take it to a tire shop to align the front end (I also changed tie rods). The shop is close by and I hope to align the wheels so I can then try and nurse the car to my indie. The car runs perfect. I'm guessing that maybe I was too heavy handed with the cleaner and maybe the MAF finally dried out. I drive the car out to the indie (about 15 miles) to leave it so he can start first thing in the morning and again the car runs perfect. Of course the cars behaves at the indie so all he does is change the fuel filter, cleans the throttle body and runs some injector cleaner thru the car. I pick up the car, runs fine. My wife drives the car about 400 miles from LA to San Francisco with no issues. My daughter drives it a few days and no issues. Then today, she is idling at a stop, foot on the brake, and the engine surges in waves up to about 2000 rpm. She holds the car back with the brakes. Then the rpms drop back to a normal 400 and everything is fine. She did not note any idiot lights.

Any ideas? And any suggestions for a reputable shop in the San Francisco area?

Thanks,

glenmore

1990 LS400

1991 300CE

2000 C280

[Alexander the o.k.]

Thanks for the update GM. Let us know what it turns out to be.

[glenmore]

I am not encouraged. I did a search on "iacv" and there are a lot of stories of low rpms and dying and none of them seemed to have been solved despite throwing caps, rotors, plugs,wires, maf, iacv, iscv at the problem.

I hope I find a good mechanic in Frisco/Berkeley.

glenmore